Bump puppet-boxen from 1.3.0 to 2.3.1

This adds a bunch of new Puppet types and some other improvements.

Full list: https://github.com/boxen/puppet-boxen/compare/1.3.0...2.3.1
Include the puppet-repository module
Merge pull request #9 from alphagov/bump-puppet-boxen

Bump puppet-boxen from 1.3.0 to 2.3.1